Infra-red (IR) radiation: electromagnetic radiation of wavelengths between about 0.75 µm and 15 µm. This is broken down into four wavelength regions

Near-IR: 0.75-1.4 µm (OLCI Oa12 to Oa21, SLSTR S3 and S4 channels)

Short-Wave IR: 1.4-3 µm (SLSTR S5 and S6 channels)

Medium-Wave IR: 3.8 µm (SLSTR S7 and F1 cannels)

Long-Wave IR: 8-15 µm (SLSTR S8, S9 and F2 channels)

Ground Control point or Correlation point: landmark, visible and located on two images, where local residual mis-registration between these images is estimated by a matching process.

Earth Surface: the Earth surface is modeled as a Digital Elevation Model (GETASSE30 provided as CFI) on top of the WGS84 ellipsoid model.

(Direct) Geolocation function: function that maps a point (k,j) (possibly non-integers) in an image to a point (x,y,z) on the ellipsoid surface. It is subtended by a model of the line of sight coming from point (k,j).

(Direct) Ortho-rectified geolocation function: function that maps a point (k,j) (possibly non-integers) in an image to a point (x,y) on the Earth's surface, by taking into account a Digital Elevation Model (DEM) z = DEM(x,y). Theoretically (x,y,z) is the intersection of the line of sight coming from (k,j) with the Earth surface modelled as a DEM on top of a reference ellipsoid. The terrain point location is corrected from the relief effect, compared to the one computed with the direct geolocation function.

Restituted value: value retrieved when all known corrections have been applied.

(Mis-)Knowledge Error: residual error when all known corrections have been applied. The true value is given by adding the (unknown) (Mis-)Knowledge Error to the restituted value.

Inter-channel spatial co-registration, simply referred to here as co-registration or misregistration: The definition is: maximum equivalent ground distance between the positions of all pairs of spatial samples acquired in two spectral channels and related to the same target on Earth.

Frame: the set of measurements acquired by the OLCI instrument at a given time

Coastal zone: sea surface extending from the coast up to 300 km offshore

Ancillary data: a classical definition is 'All on-board data, other than observation and HKTM data, necessary for the product processing'. This would include in particular not only various parameters and settings but also satellite data such as OBT and time correlations if needed, navigation data, etc.

Auxiliary data: data necessary to some steps of the product processing that are either provided by internal databases and/or facilities of the PDGS (e.g. the parameters, the calibration and the static data bases), or by external entities to the SENTINEL-3 system (e.g. meteorological data).

Search window: small window (grid) centered on a ground control point in OLCI geometry. It is a set of coordinates and is used to extract a search imagette of SLSTR channel for correlation with the context window during the inter-instrument mis-registration estimation.

Context window: small window (grid) moved around the search window (along shift vectors) in OLCI channel geometry. It is a set of coordinates and is used to extract a context imagette of OLCI channel for correlation with the search chip during the inter-instrument mis-registration estimation.

Context imagette: the radiometric counterpart of the context window, obtained by extracting the OLCI channel radiometry corresponding to the context window. If C is a Context imagette W(C) represents the corresponding context window.

Search imagette: the radiometric counterpart of the search window, obtained by resampling the SLSTR channel radiometry to the search window. If S is a Search imagette W(S) represents the corresponding search window.

Orbital Revolution Number: this number identifies the SENTINEL-3 orbit within the orbital cycle. There are 385 orbits per cycle, so the Orbital Revolution Number is between 0 and 384.

Orphan pixels or Removed pixels: These are pixels acquired by the instruments but not retained in the Level-1B gridded image, due to the Level-1B (nearest neighbour) projection on the product grid. For OLCI those pixels mainly come from overlapping areas between adjacent camera modules. For SLSTR they may come from a possible oversampled acquisition at nadir of the nadir-view, with respect to the Level-1B image gridding. In oblique view there are many orphans due to scan-to-scan along track overlap. To answer the Level-1C requirements, all those pixels are retained in Level-1B products but not gridded. Note: The expression 'orphan pixel' is used in SLSTR documents while 'removed pixel' is used in OLCI documents. The term 'ungridded pixels' is also used instead of orphan or removed pixels in this document.

Scan: a scan is defined as a complete rotation of the SLSTR scan mirrors.

Instrument scan or scan trace: the trace of a single SLSTR detector element on the ground. Thus for example in the thermal channels each detector has two elements, and so a single scan will give two scan traces, displaced by 1 km in the along track direction. Adjacent scan traces represent adjacent 'rows' of the instrument grid.

Image scan: a line of pixels in the SLST Level-1B product. Note that in the Level-1C product an image scan and an instrument scan should refer to the same thing.

Deformation model: in Level-1C processing this term refers to the interpolation model applied on the (potentially) irregular grid of ground control points and representing the deformation field between OLCI and SLSTR in the OLCI geometry.

Correspondence grids: These grids are the main output of Level-1C processing, stored in the mis-registration data files in the Level-1C product. These are grids that link any OLCI pixel in the reference band to the corresponding sub-pixel location in the other OLCI and SLSTR bands such that if a detector were placed at the sub-pixel location it would have seen the same target on Earth as the reference pixel.